Schedule II - (Notes to Condensed Financial Statements) (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Long-term debt principal amount purchased	$ 308
Fair value of securities pledged as collateral	280	$ 282
Securities posted as collateral to derivative counterparties	$ 159	$ 214
MBIA Inc. Senior Notes [Member]
Long-term debt, interest rate	5.70%
Long-term debt, maturity year	2034
Mbia Inc. Debentures [Member]
Long-term debt principal amount purchased	$ 13
Long-term debt, interest rate	7.00%
Long-term debt, maturity year	2025
6.400% Senior Notes due 2022 [Member]
Long-term debt principal amount purchased	$ 115
Long-term debt principal amount purchased, par value	100.00%
Long-term debt, interest rate	6.40%	6.40%
Long-term debt, maturity year	2022
6.625% Senior Notes due 2028 [Member]
Long-term debt, interest rate	6.625%
Long-term debt, maturity year	2028
Debt Instrument, Face Amount	$ 5
7.15% Senior Notes due 2027 [Member]
Long-term debt, interest rate	7.15%
Long-term debt, maturity year	2027
Debt Instrument, Face Amount	$ 1
MBIA Inc. [Member]
Liquid assets	239
Fair value of securities pledged as collateral	280	$ 282
Securities posted as collateral to derivative counterparties	159	214
National [Member]
Dividends from subsidiaries	60	$ 81	$ 134
National [Member] \| Mbia Inc. Debentures [Member]
Long-term debt principal amount purchased	$ 10

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